Air-conditioning control system for automotive vehicles

Abstract

An air-conditioning control system for automotive vehicles, comprising a compressor variable in capacity in accordance with a change in suction pressure thereof. A controller is provided which carries out demisting control, on the basis of output signals from various sensors, in such a manner that, when outdoor-air temperature is equal to or lower than a predetermined value and at the same time the air-conditioning control system is in the indoor-air recirculating mode, the suction pressure set by the controller is lowered to a value at which temperature on the outlet side of an evaporator is brought to a value equal to or lower than a predetermined freezing temperature, and when a state in which freezing of the evaporator may occur has continued for a predetermined period of time, the set suction pressure of the compressor is raised until the temperature on the outlet side of the evaporator is brought to a value equal to or higher than a predetermined non-freezing temperature.

What is claimed is: 
     
       1. An air-conditioning control system for automotive vehicles, comprising: a variable capacity compressor variable in capacity in accordance with a change in suction pressure thereof;   an evaporator having an outlet side;   control means arranged outside of said compressor for supplying said compressor with an electric signal for setting the suction pressure;   first sensor means for detecting outdoor-air temperature;   second sensor means for detecting whether or not the air-conditioning control system is in an indoor-air recirculating mode;   third sensor means for detecting temperature on the outlet side of said evaporator;   fourth sensor means for detecting the suction pressure of said compressor; and   said first through fourth sensor means being connected to said control means;   said control means carrying out the below-mentioned demisting control, on the basis of output signals from the respective first through fourth sensor means: (i) when the outdoor-air temperature is equal to or lower than a predetermined value and at the same time the air-conditioning control system is in the indoor-air recirculating mode, the suction pressure set by said control means is lowered to a value at which the temperature on the outlet side of said evaporator is brought to a value equal to or lower than a predetermined freezing temperature; and     (ii) when a state in which freezing of said evaporator may occur has continued for a predetermined period of time, the suction pressure set by said control means is raised until the temperature on the outlet side of said evaporator is brought to a value equal to or higher than a predetermined non-freezing temperature.   
     
     
       2. An air-conditioning control system for automotive vehicles according to claim 1, wherein said state in which freezing of said evaporator may occur is a state in which the temperature on the outlet side of said evaporator is equal to or lower than said predetermined freezing temperature. 
     
     
       3. An air-conditioning control system for automotive vehicles according to claim 1, wherein said state in which freezing of said evaporator may occur is a state in which actual suction pressure of said compressor is equal to or lower than a predetermined value. 
     
     
       4. An air-conditioning control system for automotive vehicles according to claim 2, wherein the raising of said set suction pressure in response to the continued state in which freezing of said evaporator may occur is effected only for a second predetermined period of time insofar as the temperature on the outlet side of said evaporator is equal to or lower than said predetermined non-freezing temperature. 
     
     
       5. An air-conditioning control system for automotive vehicles according to claim 3, wherein the raising of said set suction pressure in response to the continued state in which freezing of said evaporator may occur is effected only for a second predetermined period of time insofar as the actual suction pressure of said compressor is equal to or lower than said predetermined valve. 
     
     
       6. An air-conditioning control system for automotive vehicles according to claim 1, including thermo-switch means connected to said compressor, said control means and said third sensor means, said thermo-switch means being operable when said demisting control is not executed, in a manner such that when the temperature on the outlet side of said evaporator is equal to or higher than said predetermined non-freezing temperature, said thermo-switch means renders said compressor operative, while when the temperature on the outlet side of said evaporator is equal to or lower than said predetermined freezing temperature, said thermo-switch means renders said compressor inoperative, thereby preventing said evaporator from being frozen.